This invention generally relates to a low insertion force electrical terminal assembly and, more particularly, to a terminal assembly having mated male and female members which are generally easy, in terms of the amount of required force, to engage while still providing a high contact normal force when engaged. Additionally, the present invention resists permanent deformation of the terminals as a result of repeated engagement and disengagement while still providing for easy "off-axis" disengagement of the terminals,
Terminal assemblies are used in a wide variety of products having electrical components. These products range from simple electrical items, such as a lamp, to those with highly sophisticated electrical systems, such as an automobile. One variety of terminal assembly uses a generally cylindrical male member and a female member which are mated together along a mating axis. Typically, the terminals are formed by bending a stamped piece of conductive material into the desired configuration. When formed by bending, common terminal materials include nickel plated tin, stainless steel and beryllium copper,
While mated terminals generally work well for their intended purposes, a number of problems can arise when the terminals are repeatedly engaged and disengaged from one other. One problem is that the terminals may become deformed as a result of this repeated engagement and disengagement. Deformation is particularly a problem when the rigid male terminal is repeatedly inserted and withdrawn from a female terminal, having a deflectable contact element within a rigid housing, either along or at an angle with respect to the mating axis. Repeated insertion and withdrawal can also result in a decreased contact normal force, a loss in electrical interface integrity, material fatigue, as well as a decrease from the designated amount of force required for disengagement of the terminals. This latter problem allows the terminal assembly to be more susceptible to inadvertent disengagement.
To maintain the proper resistance to disengagement, one solution is to create a "tighter fit" between the terminals. Another is to use less resilient materials in forming the terminals. However, both of these solutions result in an increase in the force needed to insert the male terminal into the female terminal. Unfortunately, the requirement of a high insertion force is undesirable from a product assembly standpoint.
With the above limitations in mind, it is an object of the present invention to provide a terminal assembly which can be easily engaged along a mating axis and disengaged off-axis.
Still another object of this invention is to provide a terminal assembly that maintains a high contact normal force between the terminals even after repeated engagement and disengagement of the terminals. A related object is therefore sustaining the electrical interface integrity between the terminals after repeated engagement and disengagement.
A further object of this invention is to provide a terminal assembly which exhibits a greater resistance to disengagement when being pulled apart along the mating axis than when off-axis.
In achieving these an other objects, the present invention provides a terminal assembly which has male and female terminals that are adapted for mated engagement along a mating axis. The male terminal is inserted into a female terminal having cantilevered arms. A first ramped surface of the arms is inclined toward the mating axis, proceeding from the lead end of the female terminal toward a connector end which is adapted to engage a conductive wire or other means and which defines the point at which the arms are cantilevered. The first ramped surface is defined on the arms of the female member a predetermined distance from the connector end and at a predetermined angle with respect to the mating axis.
A second ramped surface, adjacent to the first, is formed on the female member so as to define another ramp angle with respect to the mating axis. This second ramped surface, however, is inclined in a direction away from the mating axis proceeding from the lead end toward the connector end. The ramp angle of the second ramped surface is less than that of the first.
A third ramped surface is also included on the female terminal. This surface is inclined toward the mating axis proceeding from the lead end and is also angled with respect to the mating axis in an amount greater than the second ramped surface.
In the preferred embodiment, the female terminal is longitudinally divided in thirds so that the first, second and third ramped surfaces are all formed on three resilient arms. The arms operate as a means for biasing the ramped surfaces inward into contact with the male terminal. The lead ends of the arms are, therefore, freely movable while at the opposite ends they are substantially rigid and connected to one another. Accordingly, when fully engaged with the male terminal, the arms will have snapped over the male terminal and will not be in a maximum deflected condition. They will, however, be in slightly deflected condition as further discussed below.
To require different insertion and withdrawal forces, the ramp angles of the ramped surfaces can be changed as well as the distance of these surfaces along the cantilevered arm and from the fixed end of the terminal.
When the male and female terminals are being engaged with each other, the first ramped surface contacts a correspondingly angled surface on the male terminal. The inherent biasing and length of the resilient arms cooperate with the first ramp angle to provide a decreased amount of resistance during insertion of the male member. After being inserted to a certain extent, the arms of the female terminal snap over the male terminal and the second and third ramped surfaces generally circumferentially engage corresponding surfaces on the male terminal in a condition with reduced deflection.
Being a shorter distance from the connector end, the force required to bias the arms and surfaces at these locations is greater and a high contact normal force is maintained between the terminals. When the male terminal is to be withdrawn from the female terminal, if an attempt is made to withdraw the male terminal along the mating axis, an increased amount of resistance is met because of the shorter relative length of the arms with respect to the back angle of the second ramped surface and the corresponding surface of the male terminal. If, on the other hand, the male terminal is withdrawn off-axis (with respect to the mating axis) less resistance is encountered because of the change in relation of the relevant surfaces in both the female and male terminals, as well as the use of the male connector itself as a lever arm to defect at least one of the arms of the female terminal.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims taken in conjunction with the accompanying drawings.